1. Field of the Invention
The present invention relates to a vehicle and method of controlling an engine in a vehicle.
2. Background Art
An engine in a vehicle may be subject to a variety of loading conditions, some of which may be based on operation of systems within the vehicle, rather than propelling the vehicle itself. Thus, operation of an air conditioning system within the vehicle may provide an added load to the engine. For example, the engine may mechanically drive an air conditioning compressor, or may drive an alternator to provide increased electrical power for operation of the compressor.
Additional loads can also be placed on the engine when the engine is used to provide torque to an alternator or generator which is used to charge a battery. Such a load on the engine may be particularly high in the case of a high voltage battery having a large storage capacity, such as found in a hybrid electric vehicle (HEV). In situations where one or more vehicle systems apply a load to the engine, one or more engine parameters may need to be adjusted to increase the engine output. For example, an increase in the air flow provided to the engine can be used to increase the engine output torque to provide the necessary power required by the vehicle systems.
As the load on an engine is increased, the speed of the engine may change, unless a control system is in place to compensate for the increased load. One example of an idle speed control for an engine is described in U.S. Pat. No. 5,712,786 issued to Ueda on Jan. 27, 1998. The method and apparatus of Ueda is configured to provide compensation for a sudden increase in electric load during engine idle. The electric load current value that is to be outputted from the alternator is obtained, and the air intake to the engine is increased in accordance with the obtained current value. This control system is used to keep the engine idle speed approximately constant. One limitation of the method and apparatus described in Ueda is the need to quickly detect the application of the increased electric load, so that the control system can quickly respond to maintain the engine idle speed. Such a system relies on a feedback control, which may provide a slower response as compared to a feedforward control.
In many vehicles, the loads applied to the engine by the vehicle systems will be relatively independent of the operation of the vehicle itself. For example, an air conditioning system which applies a load to the engine, will apply such a load regardless of whether the vehicle is stationary or moving, or whether the transmission is in a forward, reverse, or neutral gear. In some vehicles, however, the load on the engine may be directly dependent on the operation of the vehicle. For example, in an HEV, or other vehicle that does not utilize a disconnect clutch between the engine and the vehicle wheels, some or all of the loads applied to the engine may be removed when the transmission is shifted into neutral. This may be desirable to help ensure that the engine does not inadvertently provide an output torque to the vehicle wheels when the transmission is in neutral. If, prior to shifting into neutral, the engine was subject to a particularly high loading condition, the engine speed could increase suddenly when the load is removed—i.e., when the transmission is shifted into neutral. Although it may be possible to use a feedback control system to compensate for the removal of the load on the engine, the engine speed may have already increased to an undesirably high value before the speed is adjusted.
Therefore, a need exists for a control system that utilizes a feedforward control to quickly adjust engine operating parameters when an event occurs that would facilitate a change in engine loading conditions.